*before you read this i'm not being sexist i'm just speaking from an ex Marketing perspective*
I think the creators of the animes just expect people to prefer female evil characters in general. On Facebook groups i'm in a lot more people post their favorite girls 50 times a day and never the boys, and the creative teams probably notice this. In the least sexist way possible, i believe they think more people would watch a show with a strong female evil character to a show with full male casts
It's the sad state of anime these days from what i see in the online community. More people post about Nezuko compared to Tanjiro, Rukia to Ichigo etc.